1. Field of the Invention
The present invention relates generally to prosthetic devices and, more particularly, to a fixation system for an elongated prosthesis which approximates the characteristics of the natural ligament or tendon being replaced.
Ligaments are strong, flexible fibrous cords or bands that fasten bones together Tendons are similar cords or bands that attach muscles to bones or other structures. The concept of the invention is the same whether it be in the context of a ligament or of a tendon. Therefore any reference in the text to a ligament may generally be taken to mean a tendon, and vice versa, unless the usage clearly indicates otherwise.
2. Description of the Prior Art
Since skeletal ligaments flexibly stabilize joints, they must withstand considerable amounts of force. Frequently, the skeletal ligaments are subjected to enough force to be torn or otherwise damaged, thereby resulting in instability of the joint. This results in pain and possible damage to other tissues. Although some torn ligaments can be repaired by simply sewing the torn ends together, such repair is not always possible in cases of severe damage or disease. Further, surgical repair is not always predictable and requires a healing period of minimal stress before the ligament can again be functionally useful.
The above circumstances have led to the development of a variety of artificial ligaments. A wide variety of elongated prostheses have been proposed for the repair or replacement of diseased or damaged ligaments and tendons. Examples of such prostheses, including devices to secure their ends, can be seen in any of the patents to Treace, U.S. Pat. No. 3,953,896, to Dahlen et al, U.S. Pat. No. 4,187,558, to Dore et al, U.S. Pat. No. 4,301,551, to Silvestrini, U.S. Pat. No. 4,708,132, to Parr et al, U.S. Pat. No. 4,744,793, to Kenna, U.S. Pat. No. 4,755,183, and to Goble et al, U.S. Pat. No. 4,772,286.
Although prosthetic ligaments have a variety of outward appearances, they commonly consist of a flexible longitudinal material having two end portions. The end portions are used to firmly attach the ligament to two adjoining bones such as, for example, the lower femur and the upper tibia. In use, the flexible central portion of the prosthetic ligament is subjected to repeated flexing, stress, and, in some cases, abrasion against bone edges. This can result in deterioration and possible rupture of the prosthesis.
One of the significant problems associated with the design of an artificial ligament or tendon prosthesis is the proper design of the means for fixation of the prosthesis to the patient's bone structure, typically with the prosthesis in a state of pretension. Such a fixation device should be securely held to the bone and should be capable of firmly gripping a portion of the prosthesis without damaging it. In particular, it is important that the prosthesis and fixation device not interact in use in such a way as to significantly detract from the inherent fatigue resistance of the active prosthesis structure itself. This may occur, for example, by excessive abrasive wear between the prosthesis and the fixation device.